Field of the Disclosure
The present disclosure relates to a cuff-pressure control device, a cuffed tracheal tube, a respirator, and an obstruction detection method. More specifically, the present disclosure relates to a cuff-pressure control device used for adequately maintaining the internal pressure of a cuff, a cuffed tracheal tube and a respirator including the cuff-pressure control device, and an obstruction detection method.
Description of the Related Art
In the medical field relating to a respirator and the like, tracheal intubation is known in which an operator, such as a doctor, inserts a tracheal tube in a windpipe of a subject (mainly the human body) from the oral cavity or the nasal cavity to secure the airway and oxygen is supplied to the lungs through the tracheal tube. If a gap is formed between the tracheal tube and an inner wall of the windpipe during the tracheal intubation, secretions, such as saliva and gastric juice, may flow into the windpipe, and as a result, the subject may develop the respirator associated pneumonia. To prevent such inflow of secretions, a cuff is provided on an outer wall of the tracheal tube.
A cuff is a bag-shaped member that is inflated by gas supplied therein. The gap between the tracheal tube and the inner wall of the windpipe can be closed by inflating the cuff through the supply of the gas from an air pump into the cuff through a connection path. This can prevent the secretions from flowing into the windpipe.
However, when the cuff pressure exceeds a predetermined range, the inflated cuff presses the blood vessels in the mucous tissue of the windpipe. When the blood vessels are pressed, an ischemic state is brought about, and as a result, for example, necrosis or bleeding may be caused. In contrast, when the cuff pressure falls below the predetermined range, the cuff is insufficiently inflated. Consequently, a gap is formed between an outer peripheral surface of the cuff and the inner wall of the windpipe, and secretions, such as saliva and gastric juice, sometimes flow into the windpipe.
For this reason, it is necessary to monitor and control the internal pressure of the cuff so that the internal pressure falls within the predetermined range. For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2011-194222) discloses a cuff-pressure control device that controls the internal pressure of a cuff so that the internal pressure falls within a predetermined range.
It is difficult to directly measure the internal pressure of the cuff disposed inside the windpipe. Hence, in normal cases, the internal pressure of the cuff is indirectly measured by measuring the internal pressure of a connection path for connecting an air pump and the cuff with a pressure sensor. For this reason, if a connection tube that forms the connection path is obstructed by, for example, bending, the internal pressure of the cuff cannot be monitored precisely. Therefore, it is preferable that the cuff-pressure control device should also have the function of detecting the obstruction of the connection tube.
When the connection tube is obstructed during the operation of the pump, the internal pressure of the connection path becomes higher than usual. Hence, one conceivable method is to detect the obstruction of the connection tube by sensing this pressure change with the pressure sensor. However, for example, when the obstruction occurs in a portion of the connection tube near the cuff, the capacity of a space (connection path) measured with the pressure sensor is decreased by only the value nearly corresponding to the capacity of the cuff, and this decrease amount is smaller than that of the capacity of the relatively long connection tube or the like. For this reason, the increase amount of the internal pressure of the connection path when obstructed is also small, and may be included in measurement errors. Therefore, there is a fear that this method cannot reliably detect the obstruction of the connection tube.
Further, Patent Document 2 (Japanese Patent No. 4175664) discloses a method for detecting the obstruction by sensing an acoustic reflected wave of a pressure pulse in a pneumatic tourniquet system. However, this system needs, for example, a pressure-pulse generating means and a reflected-wave sensing means, and this increases the size and cost of the system.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-194222
Patent Document 2: Japanese Patent No. 4175664